1. Field of the Invention
This invention relates to the preparation of easy processing, cross linking graft copolymers of a polyvinyl halide such as a polyvinyl chloride polymer having improved thermal processability, improved solubility in organic solvents, improved adhesion to organic and inorganic surfaces. The branched chain graft copolymers of the invention are useful in the production of films, coatings and molded articles. The products can be produced using the usual polyvinyl halide processing equipment.
As is well known graft polymers can be prepared by reacting a monomer or monomers onto a polymer chain so that the graft polymer product contains a branched chain structure. Such graft polymers differ from straight chain terpolymers prepared by reacting only monomers in admixture.
It is known to produce straight chain vinyl halide terpolymers such as a terpolymer of vinyl chloride, vinyl acetate and maleic acid, by emulsion and suspension polymerization processes. Such products show improved processability over polyvinyl chloride homopolymers, improved adhesion to organic or inorganic surfaces, increased solubility in organic solvents and are produced by conventional polymerization processes in which maleic anhydride is not used but rather maleic acid. Such systems show far less reactivity than the graft polymerization process of the invention in which maleic anhydride is used. These methods of producing straight chain terpolymers result in very slow reactivity of the monomers and thus a reasonable conversion rate from aqueous, emulsion, suspension or solution systems cannot be obtained with desirable economy. In addition, such straight chain terpolymers based upon maleic acid are not readily cross-linkable so as to obtain polymers having reduced organic solvent solubility. By contrast, the graft polymers of the invention can be readily cross-linked since the anhydride group of the branched chain terpolymer of the invention can be reacted with cross-linking agents.
2. Description of the Prior Art
In U.S. Pat. No. 2,147,154 there is claimed a method of producing a straight chain polymerization product of vinyl chloride by emulsion polymerizing said vinyl chloride with 0.5 to 3 percent of an alpha, beta-unsaturated carboxylic acid. It is disclosed that vinyl chloride can be polymerized alone or in admixture with vinyl esters such as acrylic acid esters, acrylic acid, nitriles, or styrene. The polymerization can be conducted in mass. The emulsion polymerized product is subsequently treated with a strongly alkaline material in a liquid medium adjusted to a pH of 7.5 to 12.
U.S. Pat. No. 2,462,422 relates to the emulsion polymerization of a straight chain polymer comprising vinyl chloride, vinyl acetate, and maleic anhydride.
The object of the present invention is to develop a process for the preparation of branched chain polymers and copolymers of vinyl halide which would be extremely rapid even at moderate temperatures. It is apparent that water present in an aqueous graft or suspension graft polymerization system would decompose the maleic anhydride to maleic acid and thereby result in a slower rate of polymerization than can be obtained in the bulk process of graft polymerization disclosed in the instant invention.